This invention relates to a device comprising a pair of engaging friction elements in general, and particularly to a friction brake or to a friction clutch, having a first friction element which consists of friction materials containing organic binding agents and which suffers a greater wear and a second friction element which suffers a lower wear and consists of iron material.
Friction devices such as friction brakes or friction clutches are used in order to reduce and eventually eliminate relative movement between two parts when in use. While accomplishing this purpose, they transform kinetic energy into heat, e.g. when braking a part in motion.
When used for braking a vehicle, the friction device used may be constructed as a disc brake arrangement consisting of a brake disc and of brake linings. The extent of wear of these cooperating elements will vary in dependence on the materials chosen for the elements frictionally engaging each other and will be influenced by various secondary factors such as the friction coefficients and behavior at different temperatures. Cast iron will e.g. be used as the material for the brake disc. The brake linings are generally made of organic-bonded friction materials which usually consist of organic binding agents such as cross-linked synthetic resins such as phenolic resins, and possibly of natural and synthetic caoutchouc as well as of fillers. The fillers used may be metal chips, metallic oxides and/or other mineral materials.
If the wear is kept down as far as possible, one will achieve either a longer life or small dimensions of the elements and thus a reduced weight of the device.
For the purpose of reduction of wear, arrangements have become known where a metallic braking element such as e.g. a brake disc is provided with a long-wear coating. A process for preparing such a coating is disclosed in the German published patent application DE-OS No. 21 66 949 according to which a long-wear frictional coating is applied to each of the elements by means of a plasma jet. In this process, particles of metal, an alloy, or a combination of metals and their compounds such as metallic oxides or metallic carbides are introduced into the plasma jet. The long-wear coating in this process must have the original crystallographic properties of the particles, i.e. a hexagonal crystal system. The materials used for the production of the two coatings of this type which are in frictional engagement with each other are required to be different; one of the coatings e.g. is made based on carbides while the other is produced on the basis of oxides.
In this known arrangement an important disadvantage is to be seen in the fact that both friction elements have to be provided with a coating.
It is further known to increase the wear resistance of the brake linings. This can be achieved e.g. by using metallic-bonded brake linings instead of organic-bonded brake linings. The metallic-bonded brake linings contain particles in a sintered metallic bond.
A further method of increasing the resistance to wear of the brake linings is disclosed in the German published patent application DE-OS No. 24 06 242. There, an electrostatic coating process is disclosed by means of which thin coatings of metallic mineral powder are produced which are firmly bonded to a metallic carrier plate.
In these two last-mentioned processes or arrangements, respectively, a particular disadvantage is to be seen in the fact that while there is indeed a wear reduction with regard to one of the friction elements, i.e. of the brake lining, the other friction element, that is the brake disc, will suffer a greater degree of wear. Thus, the small permissible extent of wear of the disc will soon be surpassed.